- there are many different types of semiconductor materials which are often classified by their groups and other , but all have slightly different properties.

These different types of semiconductor have slightly different properties and lend themselves to different applications in various forms of semiconductor devices.

Some may be applicable for standard signal applications, others for high frequency amplifiers, while other types may be applicable for power applications and harsh environments or others for light emitting applications. All these different applications tend to utilise different types of semiconductor materials.

Semiconductors types / classifications

There are two basic groups or classifications that can be used to define the different semiconductor types:

Intrinsic material: An intrinsic type of semiconductor material made to be very pure chemically. As a result it possesses a very low conductivity level having very few number of charge carriers, namely holes and electrons, which it possesses in equal quantities.

Extrinsic material: Extrinisc types of semiconductor are those where a small amount of impurity has been added to the basic intrinsic material. This 'doping' uses an element from a different periodic table group and in this way it will either have more or less electrons in the valence band than the semiconductor itself. This creates either an excess or shortage of electrons. In this way two types of semiconductor are available: Electrons are negatively charged carriers.

N-type: An N-type semiconductor material has an excess of electrons. In this way, free electrons are available within the lattices and their overall movement in one direction under the influence of a potential difference results in an electric current flow. This in an N-type semiconductor, the charge carriers are electrons.

P-type: In a P-type semiconductor material there is a shortage of electrons, i.e. there are 'holes' in the crystal lattice. Electrons may move from one empty position to another and in this case it can be considered that the holes are moving. This can happen under the influence of a potential difference and the holes can be seen to flow in one direction resulting in an electric current flow. It is actually harder for holes to move than for free electrons to move and therefore the mobility of holes is less than that of free electrons. Holes are positively charged carriers.

Semiconductor material groups

Most commonly used semiconductor materials are crystalline inorganic solids. These materials are often classified according to their position or group within the periodic table. These groups are determined by the electrons in the outer orbit the particular elements.

While most semiconductor materials used are inorganic, a growing number of organic materials are also being investigated and used.

Semiconductor materials list

There are many different types of semiconductor materials that can be used within electronic devices. Each has its own advantages, disadvantages and areas where it can be used to offer the optimum performance.

Material

Chemical Symbol / formula

Group

Details

Germanium

Ge

IV

This type of semiconductor material was used in many early devices from radar detection diodes to the first transistors. Diodes show a higher reverse conductivity and temperature coefficient meant that early transistors could suffer from thermal runaway. Offers a better charge carrier mobility than silicon and is therefore used for some RF devices. Not as widely used these days as better semiconductor materials are available.

Silicon

S

IV

Silicon is the most widely used type of semiconductor material. Its major advantage is that it is easy to fabricate and provides good general electrical and mechanical properties. Another advantage is that when it is used for integrated circuits it forms high quality silicon oxide that is used for insulation layers between different active elements of the IC.

Gallium arsenide

GaAs

III-V

Gallium arsenide is the second most widely used type of semiconductor after silicon. It is widely used in high performance RF devices where its high electron mobility is utilised. It is also used as substrate for other III-V semiconductors, e.g. InGaAs and GaInNAs. However it is a brittle material and has a lower hole mobility than Silicon which makes applications such as P-type CMOS transistors not feasible. It is also relatively difficult to fabricate and this increases the costs of GaAs devices.

Silicon carbide

SiC

IV

Silicon carbide finds uses in a number of applications. It is often used in power devices where its losses are significantly lower and operating temperatures can be higher than those of silicon based devices. Silicon carbide has a breakdown capability which is about ten times that of silicon itself. Forms of silicon carbide were types of semiconductor material that were used with some early forms of yellow and blue LEDs.

Gallium Nitride

GaN

III-V

This type of semiconductor material is starting to be more widely in microwave transistors where high temperatures and powers are needed. It is also being used in some microwave ICs. GaN is difficult to dope to give p-type regions and it is also sensitive to ESD, but relatively insensitive to ionising radiation. Has been used in some blue LEDs.

Gallium phosphide

GaP

III-V

This semiconductor material has found many uses within LED technology. It was used in many early low to medium brightness LEDs producing a variety of colours dependent upon the addition of other dopants. Pure Gallium phosphide produces a green light, nitrogen-doped, it emits yellow-green, ZnO-doped it emits red.

Cadmium sulphide

CdS

II-VI

Used in photoresistors and also solar cells.

Lead sulphide

PbS

IV-VI

Used as the mineral galena, this semiconductor material was used in the very early radio detectors known as 'Cat's Whiskers' where a point contact was made with the tin wire onto the galena to provide rectification of the signals.